The present invention relates, in general, to sensors, and more particularly, to a novel coplanar resonator sensor.
Previously, microwave resonators have been used for a variety of sensor applications including sensors for measuring the thickness of materials. These prior sensors typically utilize two parallel conductors wherein the material to be measured is inserted between the two conductors. The conductors and the material to be measured form a capacitor that controls the frequency of an R.F. oscillator. Because the material to be measured is positioned between the parallel conductors, the type of material effects the amplitude of the output signal from the oscillator. Often, the material to be measured is a mixture of two components. As the ratio of the two components varies, the amplitude of the output signal from the oscillator also varies. The oscillator output signal amplitude can vary by up to 40 to 45 db for some material variations. In order to reduce the amplitude variations, the output signal of the oscillator is applied to a power limiter circuit prior to applying the signal to other circuits. The power limiter circuit increases the cost and the complexity of a system utilizing the sensor.
Accordingly, it is desirable to have a sensor that does not require positioning the material to be measured between the conductors of the sensor, and that has an output signal variation of less than 40 db as the components of the material to be measured varies.